1. Field of the Invention:
This invention relates in general to earth drilling equipment and in particular to rotary power slips mounted concentrically with the pipe opening in a rotary drilling table.
2. Description of the Prior Art:
U.S. Pat. No. 4,333,209 (Herst), entitled "Rotary Power Slips", issued on June 8, 1982, discloses rotary power slips having a housing mounted in a rotary table of an earth drilling rig. Air, from a stationary fluid source on the drilling rig, is transferred to pneumatic cylinders in the housing to operate the slips. A perforated annular bladder is expanded to form an expansive fluid duct between a stationary seal ring, connected to the stationary fluid source, and an air transfer plate, which rotates with the housing.
After the slips have been raised by the cylinders, the fluid pressure is cut off, releasing fluid pressure to the cylinders from the stationary source and the seal ring disengages. In prior art devices,such as Herst, mechanical means are used to lock the slips in the raised position. Such mechanical means are subject to jolts and vibrations common to drilling floors. An improved apparatus was needed to lock the slips in the raised position.
In addition, improvements were needed in the rotary power slips, so that the power slips will take more abrasion, leak less, and take more pneumatic pressure. Also, it was desired to provide a seal ring which will be simplier and faster to replace under field conditions.